It is frequently necessary to grind surfaces and surface regions of cutting tools to precisely predetermined dimensions. This is especially so for stepped tools of all kinds, for example drilling tools, drills with stepped diameters, reamers, milling tools in general, end mills, circumferential mills, roll-over milling tools, and the like.
Briefly, the tools for which the present invention is especially applicable are stepped tools with straight, spiral or angular grooves or flutes, step drills with straight spiral or angular flutes and made of high-speed steel, carbide, or with brazed cutting edges; reamers and step reamers with straight, spiral or angular flutes; end mills having cylindrical and/or conical chip removal grooves of various shapes; milling cutters in general, and especially side milling cutters, hobbing tools. All the tools are made of high-speed steel, carbide, ceramic, or other materials used in cutting tools, or may have brazed-on cutting inserts. The surface quality of the surfaces of such tools should be as good as possible and the dimensions of the tools should be highly accurate.
In the specification that follows, the term "cutting tools" will be used generically for any and all of the above tools for which the present invention is especially applicable.
Grinding processes are used for manufacturing cutting tools, as well as to sharpen cutting tools which have been used. For grinding, a grinding element, for example a grinding disk (also known as a grinding wheel), is engaged with the respective cutting tool. A not insignificant engagement pressure is exerted by the grinding element on the cutting tool. Generally, the engagement pressure acts more or less perpendicularly to the outer circumference of the cutting tool. The cutting tool can be rotated about its longitudinal axis, so that the grinding element covers the entire circumference of the cutting tool. In this axial rotation, the cutting tool is engaged only intermittently by the grinding element due to the presence of the chip removal flutes or grooves, or by other recesses which may be formed in the cutting tool. When the grinding element is facing such a flute, groove or recess, it runs freely. When the cutting tools have relatively large flutes or recesses, the grinding tool is in engagement with the cutting tool only for a fraction of the overall time during which the grinding operation takes place. The non-grinding time is used up by the grinding element running free, for example when it is opposite a chip removal flute located between the cutting surfaces or cutting surface portions of the cutting tool which are actually to be ground.
Comparatively long cutting tools, such as drills, boring tools, reamers, and the like, have slight lateral, that is, radial resilience or elasticity which may lead to problems with regard to accuracy of the grinding. If the cutting tool deflects only slightly when the grinding element, typically a grinding disk, is in engagement with the surface region to be cut, the surface which will be ground will no longer be precisely cylindrical but, rather, slightly bulged or eccentric or barrel-shaped, or otherwise deviates from an ideal design shape and size. Precision tools have diameter tolerances in the region of 1 .mu. meter. Such deflections, thus, may lead to quality problems.